1. Field of the Invention
The invention relates to a television receiver and, more particularly, to a digital television receiver.
2. Related Background Art
In recent years, a memory is the nucleus of the electronics industries such as computer, computer concerned equipment, video disc, digital audio disc, and the like. The development of a memory material is extremely actively executed. Although the performance required for the memory differs depending on the application, a high response speed in recording or reproduction is indispensable. Hitherto, a semiconductor memory made by a material of semiconductor or a magnetic memory made by a magnetic material is a main memory. In recent years, however, a cheap recording medium of a high density by means of an optical memory using an organic thin film such as organic pigment, photopolymer, or the like has been proposed with the advancement of the laser technique.
On the other hand, a scanning tunneling microscope (STM) capable of directly observing an electron structure of the surface atom of a conductor has been developed. A wide application is expected because of the following reasons (G. Binning et al., "Phys. Rev. Lett.", 49, 57, 1982).
(1) A real space image can be observed at a high resolution irrespective of a monocrystal or amorphous. PA1 (2) There is an advantage such that the real space image can be observed at a low electric power without giving a damage by a current to a sample. PA1 (3) The STM can be operated even in the atmosphere and can be used for various kinds of materials.
According to the scanning tunneling microscope, in a state in which a voltage is applied between the probe (metal probe) and the conductive material, when the probe is allowed to approach a position of a distance of about 1 nm from the surface of the conductive material, a tunneling current flowing between the probe and the surface of the conductive material is used. The magnitude of the tunneling current is very sensitive to the distance between the probe and the surface of the conductive material, and exponentially functionally varies in response to such a change in distance. Therefore, the probe is relatively and two-dimensionally scanned over the surface of the conductive material while the distance between the probe and the surface of the conductive material is controlled so as to keep the tunneling current constant, whereby the surface structure (concave and convex portions of the surface) of the real space of the conductive material can be measured. Various kinds of information regarding all of the electron clouds of the surface atoms can be also read. A resolution in the in-plane direction of the conductive material at this time is equal to about 0.1 nm.
By applying the principle of the scanning tunneling microscope, high density recording and reproduction can be executed sufficiently on the atomic order (subnanometer). For example, in a recording and/or reproducing apparatus disclosed in Japanese Patent Laid-Open Application No. 61-80536, by eliminating the atomic particles adsorbed on the surface of the recording medium by an electron beam or the like, recording information (data) is recorded (written) or the recorded information is reproduced (read out) by the scanning tunneling microscope. There has also been proposed a method whereby a thin film layer of a material (for instance, organic compound or chalcogen compound class having a conjugate .pi. electron system) having a memory effect to the switching characteristics of a voltage current is used as a recording layer and the recording and reproduction are executed by the scanning tunneling microscope (refer to Japanese Patent Laid-Open Application No. 63-161552, Japanese Patent Laid-Open Application No. 63-161553). According to this method, when a size of recording bit is set to 10 nm, the recording and reproduction of a large capacity of up to 10.sup.12 bits/cm.sup.2 can be performed.
As a scanning mechanism of the probe, a cantilever type has been proposed (Japanese Patent Laid-Open Application No. 62-281138). Several tens of cantilever type scanning mechanisms made by SiO.sub.2 having a length of 100 .mu.m, a width of 10 to 20 .mu.m, and a thickness of about 0.5 .mu.m can be formed on the same silicon substrate. A writing circuit and a reading circuit are also integrated on the same silicon substrate.
In recent years, digitization of television receivers and video tape recorders (VTR) is being progressed. As reasons of it, the advancement of the recent digital technique and the pursuit of high image quality and high sound quality at the level of industrial articles can be mentioned. That is, in the conventional analog recording, there are limitations of the S/N ratio and waveform distortion of the reproduction signal, and limitations are given to the picture quality of the reproduced image and the sound quality of the reproduced voice. In the digital recording, however, the picture quality of the reproduced image and the sound quality of the reproduced voice are determined by only the A/D converting characteristics and the D/A converting characteristics and are not directly influenced by the characteristics of the tape and head, so that those qualities are remarkably improved. Further, by providing a memory, the delay of signal or the like can be easily performed. Therefore, the elimination of noises such as ghost or the like and the improvement of the picture quality by a non-interlacing system or the like which are fundamentally based on the arithmetic operation of numerical value data can be also realized. With respect to the advancement of the digital technique, the realization of a high processing speed of the circuit is progressed due to the advancement of the semiconductor technique and an A/D converting speed is remarkably improved. Therefore, it is also possible to sample at a frequency of about 100 MHz. In association with it, an arithmetic operating speed of the semiconductor device is also extremely so high to be 1 nsec per gate and more complicated image processes can be also executed at a high speed.
A high picture quality and a high sound quality are realized by the above digitization in a television receiver and various functions are added as accessories. For example, a 2-picture plane display, a multi-picture plane display, a still image display, a frame dropping display, and the like can be mentioned as main functions. A recording capacity of up to a few fields or a few frames is enough to execute signal processes which are necessary for such functions from a viewpoint of a recording capacity. A target to be processed is also limited to only the image signal of one channel from a problem of transfer speed.
In the television signal of the existing NTSC system, since a frequency band of the image signal is limited to 4.2 MHz, a frequency of about 14 MHz is needed as a sampling frequency of the image signal. Therefore, now assuming that the number of quantization bits is set to 8 bits, in the case where the image signal was sampled as it is, a data transfer speed of 110 Mbps or more is needed. Even if the image signal was properly compressed, a data transfer speed of about 20 Mbps is necessary.
As mentioned above, since a very large recording capacity and a high data transfer speed are necessary to record the image signal, a memory of an extremely large recording capacity is necessary in order to execute the signal process of a long time base. For example, even in case of using a magnetooptic disc or a laser disc, which are at present general recording media of a high density, in order to record the image signal of 10 channels at a data transfer speed of 20 Mbps for about one hour, 500 or more magnetooptic discs are necessary and its data transfer speed is equal to 200 Mbps. It is, consequently, very difficult to use such a recording medium as a buffer memory.